I always start with the movement speed for Nasus. His starting speed is like watching grass grow, so if you want to get anything done, I suggest tech'n up to the Boots of Swiftness. With this, you can play positional Support, which will help your lane a great deal. Defense early with Nasus seems to be a great way to play him while first starting out.

Getting a Mana boost is really important for Nasus. Nasus is pretty mana heavy, so the more mana you have, the better. I always tech up to the Lich Bane. Gives good Mana and damage boost which makes Nasus' abilities while laning that much more effective. If you want to go more damage heavy without relying too much of the mana, getting the Ravenous Hydra would be GREAT for you to get early/mid game.

Nasus benefits greatly if you have a good ally in your lane. He can do good on his own, but using his abilities in conjunction with your ally makes him more devastating. Getting a good damage add-on will help with this. Ravenous Hydra and the Bloodthirster are my two favorites. Depending on the game, I'll decide which item to tech too. Most of the time I end up getting the Hydra. The extra Damage won't make you formidable by any means, depending on how late in the game it is, but it will be a GREAT support for your Tanking allies.

After im done getting all of the tech upgrades that I like, I'll end up getting a heath upgrade. I almost never see time to tech too it, but when I do, Nasus becomes a small tank for your remaining allies that are attacking with you. Since I play Nasus positional and support, I usually don't catch the attention of the enemy champions until I strike for a Slay or at least do enough damage for an assist. The only health boost i get is the Warmog's Armor. Normally I will only have the beginning tech for the Armor, but it is enough to still be a formidable enemy on the field.

As I said, I play Nasus positional and support. Others can Tank him, some can Jungle with him, but I have not been able to pull that off properly enough. So I'm just sticking with what I know. While laning, get either top or bottom, depending on the map. Middle is a bit difficult for beginning players, but it can be done with the right instincts.

Nasus is an overall great champion, but I say that with reservations. If you play this build, you need to have good awareness of what is happening in your lane, as well as the jungle near your location. If you manage to get caught off-guard by enemy champions, you will almost nearly get slain. This build for Nasus is not meant to be played as a fighter or a tank, but as a support. So keeping that in mind, be careful of what is happening around you. Unless you know you can get the kill, Cast Wither (W) and fall back.
Pros: Good as a support while gaining a ton of minion kills and assists
Cons: bad with upfront confrontations early game while still trying to get your good add-on's

Make sure to keep Nasus behind your ally champions and abuse his range abilities early/mid game. Once you get the sandstorm ability, it will be much easier for you to start getting a higher number of champion kills, while also getting a ton of minion kills. In the fray of things, Nasus is a good team player while used properly. Make sure to abuse his Wither (w) while casting Spirit Fire (E) right after, letting your ally have easy clearing to take out the enemy champion. They will get the kill but you will at least get the assist. It wall changes late game when Fury of the Sands (R) combined with Siphoning Strike (Q) to roll in your champion kills.

As said before, play positional and support to abuse the ranged abilities of Nasus. That way you will still be a formidable opponent while also playing good defense with a good offense in the lane. Make sure to keep up on your mana to keep it high, and to cast your abilities often on enemy champions. They won't always die, but it will keep them at by while reinforcements arrive to help you out.

While playing Nasus, I have tried different builds: Tanking, Jungling, and Support. I found that support is the best way to play with Nasus while you Lvl up and tech up to the better gear. Make sure to have good map awareness as so you dont die to early ganks by enemy champions.

Thanks for reading, feel free to comment with suggestions and other such things.